The Science of Deduction
by 908-03
Summary: Sera Masumi has a new neighbour, he managed to deduce she is a tomboyish high school detective and some other things about her. Is he going to solve mysteries faster than any detective in the story?
1. Neighbour

Author's note: This is my first attempt at fanfiction writing, treat this as some sort of experiment.

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><p>After solving a murder case that happened at the construction site near to the hotel Sera Masumi was staying at, she returned to the hotel's elevator to get back to her room, and during the time she was in the elevator she could feel that he was staring at her. He was a young man in his late teens or early twenties, tall and lean. His blue-black bucket hat obscured his face, and he wore similarly coloured long-sleeve polo shirt and trousers. The young man was gripping a wet umbrella with his right hand, just like her.<p>

"So this right handed guy was outside for over an hour and he is returning to his hotel room just like me or he is visiting someone's room, since it had stopped raining for an hour and he uses his right hand to hold a wet umbrella", Masumi thought to herself. For the record, she was wearing her brown jacket and light blue jeans complete with the fedora she inherited from her eldest brother Akai Shuichi (the same attire she wore when she first appeared in Detective Conan).

To her mild surprise, the man left the elevator together with her. However as she walked to her room she quickly realised the man not only stayed at the same floor as her but was her new neighbour, previously the room next to hers was empty.

"Long timer?" the man tried to strike a conversation right after Masumi took out the card of her room. She simply looked at him, wondering how come he knew, before suddenly realising it was the scratches on her card.

"You are sharp, you deduced it from the scratches of my card?" she held out the card for him to see.

"These cards are regularly discarded and replaced, especially if they are scratched. Hence in order for you to be holding onto a scratched card, you must have been the one who made the scratches, in other words a long timer at the hotel. Anyway nice to meet you, high school sleuth", the man elaborated before reaching his hand out to offer.

Masumi did not reciprocate the offer of a handshake, instead her body tensed and she thought, "If you are some creepy guy who has been stalking me, prepare to get a beating. No way in hell can he deduce so much about me, at least not in with the short amount of time he has spent with me, he does not have enough information to start with. The only people capable of such deduction are her middle brother and Sherlock Holmes, but her middle brother is generally lazy and rarely tries to do so while Sherlock Holmes is a literary character from the nineteenth century."

"I can sense your vexation, allow me to explain. You have slightly uneven shoulders which are probably caused by the fact that you carry your bag one handed or may even balance the bag over and behind your lower shoulder, there are many kinds of occupation that require you to carry your bag around however there is a small callous on your right hand's middle finger. Such callouses are generally formed due to prolonged hours of writing, nowadays most author and journalist relies on computer to do most of their heavy work, the only kind of people I can think of that still writes a lot these days are students and students also carry a bag around them especially when travelling between home and school. Hence I infer that you are a high school student, the 'high school' part is simply my estimation of your age."

Masumi was out of words, suddenly he reached for her hand and grabbed it. "Pardon me. You cut your fingernails really short. Longer fingernails will press into the skin when you write fast…and looking at your palmar marks I can see you clench your fist a lot as there is a clear horizontal line across your palm. Clench your fist a lot is another reason to cut your fingernails really short, you practices martial arts, is it Jeet Kune Do?"

Masumi simply nodded as the man continued, "well the reason why I think particular martial arts you are practicing is Jeet Kune Do is because the way your body tensed ever so slightly when I tried to offer a handshake at the awkward time, I just realised at that moment you must be thinking I am some kind of a creepy stalker and was prepared to beat me up. One of Jeet Kune Do's philosophies is explosive and fluid attacks without telegraphing, if the martial art that you are practicing is something else, you would most likely be standing in some kind of a combat stance ready to kick my ass. Anyway I am glad you didn't because the only tool I can defend myself is this umbrella that I am holding."

He chuckled a little before Sera asked him how he knew that she was a detective. "You had the stench of blood and dead body on your clothes, that was how you got my attention in the elevator. There's some mud on your shoes but notably traces of mud on your knees as well, despite your best efforts to wipe it off. Notably your shirt and hat are wet even though you are also carrying an umbrella which is wet as well, in other words you were using the umbrella but for some reason forego it when the situation demands and hence get yourself wet out in the open. So during the time you left your hotel room not only were you walking and kneeling on a muddy area, you also chose not to use the umbrella you brought along with you at some point of your journey. The nearest muddy area is the construction site, in which a person had been discovered to be bludgeoned to death there only a few hours ago, although the muddy area can be anywhere such as a park considering the stench you must have been near the dead body at the construction site for prolonged period. This would also explain why you forego your umbrella and expose yourself to the rain as well as the mud on your knees, as you had to kneel down next to the dead body and use your two hands to check on the body. It would make perfect sense if you are a cop, however you are way too young to be one and according to my deduction you should be a student so I conclude you are some sleuth who stumbled upon the body."

"Impressive." It was all Masumi could manage, she was taken aback. Nevertheless she quickly recovered and now with a sudden interest in this man. "Well then, what else can you deduce about me?

"The small bags under yours eyes, some people will think you are sleep deprived however due to the lack of dark circles you are most likely born with them. Your fedora is slightly oversized and really worn, so you probably inherited it from an older sibling, parent, or someone who is like an older sibling to you. Alternatively, you bought it second-hand somehow. Anyway I presume the original owner of this fedora is male."

Without warning, the man's hand reached out again with his fingers briefly touching her jacket. "There is a single strand of light blond hair stuck on your clothes at waist level, probably due to static electricity considering the dry weather recently. It is clearly not your hair since your hair is black, it belongs to a light blond haired child whose height is around your waist level. To get the blond hair there the child must be close to you, literally and or otherwise. Since this child's height is around your waist, considering the length of this particular stand of hair I would estimate that the child has at least neck length hair."

"Bull's eye…but now is my big question, do you know my gender? Not many people can get it right when I dressed up like this"

"You are a tomboy who frequently gets mistaken for an actual boy. You hair is incredibly short, you wear rather masculine clothes and you used the pronoun 'boku' to refer to yourself, plus you are rather flat-chested and most people identify the gender of a non-child through the chest area because it is generally difficult not to make a mistake. However if they actually used their brains and look a bit lower they will realize you do have barely noticeable hips. Anyway if I want a more detailed analysis of you I can measure the ratio of your index finger to your ring finger, this is known as the digit ratio, and it is basically influenced by the ratio of testosterone and estrogen in you. Digit ratio does have some correlation to physical and behavioural traits. On an unrelated note, usually I don't flaunt my deduction to others as most people get freaked out by my deductions but since I deduced that you are a detective I inferred that you may be interested in what I can deduce about yourself."

Masumi smiled, revealing her cute crooked tooth. This time round she is the one offering the handshake, "Nice to meet you, my name is Sera Masumi, high school detective."

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><p>Author's note: So this original character of mine is bright...right? I chose not to reveal his name because at this moment it is unnecessary, treat it as some sort of cliffhanger. Do not expect me to continue it any time soon if at all, as I will need time to cook up plots and his deductions aka Sherlock Scan. Real Life may not permit me the luxuries of such time. However even if I may not continue this story any time soon please review deductions in this story, like if they make sense or not, it will help me greatly. I really hope I did not mess up the digit ratio thing. Also, English is not my first language so my work may have some grammatical errors that I did not notice<p> 


	2. Kudo Yusaku's not-cold case

So I managed to write a second chapter for this story in the end, ideas come and go so I only write this story when I am feeling really smart. This chapter is adapted from Kudo Yusaku's cold case, I decided to write this as soon as I realised there is a way to solve the case faster than the time the main characters took. I think this chapter will be easier to understand if you have read or watched the chapters/episodes before, anyway my OC will be doing an analysis of the kanji character central to this case. I have decided not to give my OC a name, what kind of writer does that? I thank my reviewer _MoonRaven95._

**DISCLAIMER: I do not own Detective Conan**

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><p>Sera Masumi, Mouri Ran and Suzuki Sonoko were walking towards their respective places of residence after school. They were talking about Kudo Shinichi's father, Kudo Yusaku.<p>

"So Kudo Shinichi-kun's father is the famous mystery writer Kudo Yusaku?"

"Yeah. Though it seems he's not in Japan at the moment, but writing abroad."

"When I was younger, I used to read his books a lot, like the night Baron series."

"Well, it's thanks to those books that his son ended up as a mystery nut."

…

The girls' conversation drifted to the bizarre case which even Kudo Yusaku seemingly had no idea about the truth, when they run into Sera Masumi's new neighbour. The neighbour was wearing the same attire when he first met Sera Masumi: bucket hat, long-sleeve polo shirt, trousers, all in a blue-black colour.

"Hello." He greeted the girls.

"Hi, I didn't expect to see you here." Masumi replied.

"I'm just out for a walk."

"Sera-san, who is this guy? Your boyfriend?" Sonoko asked and teased the female detective by whispering into her ears.

"You are?" Ran asked.

"He is my neighbour who recently moved into the room next to mine, he is really good with deduction. He could tell that I am a female high-school Jeet Kune Do practitioner and detective just by looking at me." Masumi sounded like she was happy about that fact.

"Is that really the whole story? Did he ogle at you to tell? Or did he accidentally touch your chest to tell that you are a girl and then you used Jeet Kune Do on him?" Sonoko teased her friend, "Or did you two-"

"Tsk." Masumi waved her friend away from her face before asking the man, "can you recount how you managed your deductions? I'm sure my friends here will like to hear more about it, plus I want to hear it again too, it was impressive."

"Thanks." He was a bit surprised that there are people genuinely interested in his deductions, and so he recounted in full detail about his encounter and deductions about Sera Masumi.

Listening to the man presenting his past deductions, Ran felt that he somewhat reminded her of Shinichi. However, unlike Shinichi who gleefully presents his deductions in a cocky tone when no one asked for it, the man presented his in a smooth and natural manner that sounded almost as natural as breathing.

When the man finished recalling his deductions, Sonoko asked him what he could deduce about her and Ran, but before the man could respond all of them heard a cry from another man whose voice came from a secluded alley of the street they were walking on.

"Hey, are you alright?"

"Hang in there, Takaich!"

"Takaichi-san!"

"Oi, Takaichi!"

The curious girls took a look at the secluded alley, and saw two men leaning close to another man whose body sat on the floor with his back leaning against a vending machine. One of the two men was older and the older man was wearing a tan-coloured jacket while the younger one was wearing a dark brown jacket. Sera Masumi sprang into action, running towards the three men while her two friends promptly followed her. Realising the girls just went into the alley, Sera Masumi's neighbour leisurely ambled behind.

"What happened" Ran asked.

"Well, he didn't come to work today, so we went looking for him and found him lying here." The elder man in tan jacket replied.

"There's blood dripping from his mouth too!" The younger man clad in dark brown jacket exclaimed.

"I called an ambulance just in case."

Sera Masumi was already examining the dead body, meanwhile her neighbour crouched beside her. The neighbour seemed to be closely examining at something on the ground area between Masumi and the dead man, it was the kanji '死', which was written in blood. '死' means death.

"_Blood has dried, this chap is dead for hours unless the dry blood belongs to someone else. The way this character in blood is presented is interesting. The cigarette has blood on it." _The man mentally noted.

Sera Masumi opened the left eye of the dead man, the white area of that eye was yellowish.

"He doesn't need an ambulance. It seems that he's already been dead for nine hours." Masumi announced and confirmed the man's unspoken suspicion; everyone except him opened their own mouth in surprise.

"Is he an alcoholic?" the detective inquired for confirmation of her own deduction.

"Uhh, yeah. Even though the doctor told him to stop."

"But how did you know that?"

"The whites of his eyes have turned yellow, and despite being thin, his belly is bulging out. That's ascites, which proves he had a bad liver. Furthermore, a can of beer was left untouched in the delivery bin of the vending machine. Judging from the situation, it's probably what he was trying to buy just before he died. People with bad livers usually avoid alcohol, as it makes their symptoms worse. I theorised that if he wanted to drink despite his medical conditions, he could have been an alcoholic." She explained.

"Amazing…" said Sonoko.

Masumi continued, "Having drunk alcohol, his cirrhosis caused him to vomit blood from variceal ruptures and no one was around to help him so he ended up dying on the street. This is what you'd normally think but he did not die from illness but rather due to a maliciously perpetrated crime." She then pointed to the '死' character written on the ground in blood, and Ran was quickly to realise the '死' character was the practically identical to the '死' character from the cold case of Kudo Yusaku.

After some quick discussion, the girls called the police and decided to head to Kudo Shinichi's house afterwards for further investigation on the bizarre phenomenon.

"Say, have you figured anything out." Before the trio left, Masumi asked her neighbour. She sounded like she was expecting something major or important.

The man shrugged nonchalantly, "I don't have the slightest idea." He lied.

"Ehh!" she sounded almost surprised, there was also a slight disappointment in her voice.

"Do you want to come with us? I am sure you can be of great help." Ran asked the man.

"Sorry but I have to decline your offer. I am not a detective. I will stay here till the police arrive, I can make the statements for you if necessary." He replied.

"Come'on. Let's go." Masumi told her friend, for some reason she looked a bit grumpy, much to the man's amusement.

"_My neighbour is lying. He knows something, it is impossible that he does not."_ The female detective thought.

"_Field experience is invaluable to a detective and nothing is more rewarding to reaching the truth of the mystery yourself. Let's see how long it will take you to solve this mystery, Sera Masumi."_

After he was sure that the girls were away from the scene, Sera Masumi's neighbour quickly took out a ruler and measured the dimensions of the '死' character before he measured the length of the cigarette. The two men who discovered the dead body simply looked at the hat-wearing man in bewilderment. Smirking, he then took out a few coins and placed them on the gaps in the kanji character. The neighbour was not the least bit surprised when the coins filled the gaps perfectly, while the two men who discovered the dead body gasped in surprise and amazement.

"I have solved the mystery behind '死', this is just a petty theft case."

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><p>The case was eventually solved on the teenagers' side, concluding with Masumi, Ran and Conan beating up some gangsters who decided to commit some petty theft. The tomboyish detective was walking towards her place of residence, having asked her friends to make the statements necessary for police investigations in her place. Masumi had plans in mind, for starters, she wanted her roommate to get out of her room at eat dinner together at a certain café, her roommate has been hiding in that tiny hotel room for way too long. Secondly, knowing the man lived next door to her, she would see him again sooner and later, and when she does she would force the truth out of him: what exactly did he learn at the site of the '死' character.<p>

The child with no name given opened the door of her room slightly, peering outside. She wanted to make sure the coast is clear; so as little people as possible would see her but most importantly her neighbour would not see her. The child had heard her roommate talking about this mysterious neighbour of theirs, the mentally younger of the pair rambled on about all the little details that neighbour managed to pick up and the deductions he made, even blushing slightly when sleuth revealed how he deduced the tomboy's frequently-mistaken gender correctly. The detective also mentioned she gave their neighbour her number because she wanted to contact him in the future and learn more about this unique kind of deduction in which she called it a 'scan'. The child responded by cautioning her roommate to be extra careful with such a sharp neighbour around, their neighbour had deduced not only the child's existence but her approximate height and relative hair length as well from a single strand of hair. Who knows just how much more information he can learn if he actually see the child, and he might thus get curious. At the same time, the child wondered if the neighbour is first man in history who hit on a girl with some deductions about her and the girl responds by giving him her number.

The child walked out of the hotel room, coughing, confident the coast was clear. Or so she thought, as she heard the sound she wanted to hear the least at that moment-the sound of a door opening, coming right from the room of the neighbour. Their gaze met for a moment, the man with no name given and the child with no name given. The child momentarily froze before returning to her normal composure while the man looked enlightened, he seemed to have realised the owner of the blond hair on Sera Masumi's shirt was standing right in front of him. The physically young girl was glad her roommate arrived just in time for the rescue.

"_A brief moment of panic flashed across her face, she is sprinting towards me. Maybe it has something to do with this child."_

Sera Masumi sprinted at full speed towards the man and the child once she saw them together; this was not supposed to happen.

"Hi." Sera Masumi awkwardly greeted her neighbour.

"So I presume you have solved the case and gave the thief or thieves a good beating?"

"Um…yea, but how come you…"

The man suddenly grabbed her right hand and held it under the hotel light, "Some of your right hand's fingers were slightly swollen. I presume you punched the thief or thieves really hard at somewhere with angular bones, probably the jaw."

"Then how did you learn about the thieves in the first place? Have you solved the case already?" Sera Masumi impatiently asked her neighbour.

"Yes. The man who was found dead sitting on the ground leaning against a vending machine, died of medical condition just as you initially deduced, however as soon as you saw the '死' character written on the floor in front of the body you instantly assumed this must be a case of maliciously perpetrated crime by a human being. Freak events do occur; you should not have ruled it out instantly."

Masumi reflected on how the case was closed, the man named Subaru who lived at the Kudo mansion mentioned something interesting to Kudo Shinichi over the phone and Kudo Shinichi promptly realised the truth of the case, maybe the one who solved the case was neither Kudo Shinichi nor her but that Subaru guy.

"For starters, when I saw the body I deduced the man was an alcoholic; although the route I took was slightly different from yours. I observed a thin line of calloused skin running across his right forefinger, his right palm was facing upwards after all; it was most likely formed due to repeated opening of a certain canned drink, in other words the dead man was addicted to a certain canned drink. The type of canned drink that was left there was beer, and hence by combining the two observations, I theorised he was most likely an alcoholic, after all it is rather unlikely for a person to be addicted to canned drinks in general. I noticed the bulging stomach too, although I never had the chance the check his eyes since you did that for me."

"How did you realise the mystery behind the '死' character written in blood?"

"When you see the character, have you ever considered how it is written?"

The high-school detective suddenly felt stumped, she realised she had not gave a thought to how precisely the letter in blood was written when she first saw the letter because she was too excited to think that through as much as she hate to admit it.

"There are numerous ways to write a character in blood, it can be done by just using your own fingers or it can be done with the help of a tool such as a paint brush. However, more importantly is the paint itself, the source of blood. In order to write something you will need enough blood that can be easily obtained from a source, yet the amount of blood present at the scene was minimal. There was some blood which flowed out from his mouth and on his chest and stomach, as well as a small amount of blood on his right palm, these are not locations suitable for obtaining enough blood to paint. If we assume the blood is from someone else, for instance if the culprit cut his finger and draw out '死' with the blood bleeding from his cut finger, is plausible but it would neither explain the glaring inconsistencies in the thickness of the strokes of the Kanji character nor explain why the holes (empty spaces) in the character are unusually round." The man explained.

Sera Masumi failed to realise her mouth was slightly open as she listened to her neighbour, while the child simply folded her arms and listened.

"If you studied the character closely, you would have realised the unusually round spaces, the inconsistent thickness of the strokes, and the fact that the '匕' in '死' is unusually slanted. They are great hints towards how the '死' character is written, because kanji letters are made up of straight lines and occasional curves but most importantly, they are supposed to be upright and fit nicely in a square. It is rather difficult to actually write in inconsistent strokes as well, limiting the possible tools or methods used, a paint brush and a pool of blood can theoretically achieve inconsistent strokes but as I explained earlier that has been ruled out. What tipped me off was actually the cigarette right next to the '死' character, curiously only one side of the cigarette was covered in blood, meaning the cigarette was already lying on the floor when blood sprayed onto it. Since it is impossible for the blood to only spray nicely on the cigarette, where did the rest of the blood go? Looking around I quickly realised the length and width of the gap between '夕' and '匕' are about the same as the dimensions of the cigarette, it would make sense if the cigarette occupied that gap and then rolled away. Therefore, some other objects caused the other holes to form the '死' character. Considering the fact that the man was buying canned beer right before he died, he must have his wallets and small change around. The wallet and the small change when positioned correctly can create the '死' character in tandem with the cigarette, the small change can also explain the unusually round spaces, the wallets and the small change went missing simply because someone was stupid or desperate enough to steal coins stained with blood."

"But what if he went out with just enough money to buy the beer and did not bring along his wallet, your theory would be rendered moot." The child interjected, her sentence punctuated with coughs.

"Of course if we assume the man went out with just enough change for beers and did not bring along his wallets, then my theory would be incorrect. However, the man has been outside for hours, there was dirt and sand on his pants and jacket, I assumed he was some sort of blue-collar worker who did not return home at all after the previous day at work. If he knew he was going out all day he would have brought along his wallet, wouldn't he? Furthermore, to show that this is not a maliciously perpetrated crime, there were no external wounds on the body. Even if we assume he suffered from internal injuries due to kicks or punches and then collapse against the vending machine, his clothes would have shown appropriate folds and creases, yet from what I observed from his clothes he did not violently sit down or anything of that sort. Have you discovered the coin under the vending machine?"

Masumi snapped out of her trance, "Yea…wait you knew the coin was there!" For a moment she was comforting herself that while she failed to solve the mystery behind the '死' character herself at least she was the one who discovered the incriminating evidence of the bloodied coin under the vending machine, but looks like that was not the case too.

"I found it under the vending machine as soon as I came to the realisation of what caused the '死' character, but I left it there without informing the police because I believed you would eventually solve the case and discover this important evidence before anyone else does."

"But if you already solved the case right after I left the scene you could have informed me, I gave you my number! What if the gangsters were more dangerous than what I could manage? What if they were armed? I wouldn't have to waste my time trying to figure out something already figured out, and you placed my friends and me in danger!"

"I figured since both you and that long-haired girl know martial arts you can keep yourselves safe, plus you told me you are an aspiring detective, amongst the most valuable things to an aspiring detective is field experience."

Masumi was not sure exactly how to retort her neighbour, instead she simply asked "How did you know Ran practises martial arts as well? She did not attempt to attack you or anything close to that, unlike my case."

"The girl has a deceivingly slender frame, but her arms and legs are athletic and lean, so I inferred she is physically fit. She also stands and walks upright with her legs aligned with her shoulders from top-down. From my past observations about other people, soldiers and people trained in martial arts tend to do that, she is too young to a soldier anyway so I assumed she must have learned some form of martial arts."

"I can't help but to wonder where your eyes are looking at when you see a girl, you noticed at my hips to tell I am a girl and you noticed at Ran-chan's legs…anyway what if you are wrong about Ran-chan knowing martial arts? In addition, Sonoko, the brown-haired girl, does not know martial arts. The results could be disastrous, Sonoko was in fact held hostage." Masumi argued while giving her neighbour that grumpy face again.

"Don't make that kind of face, you three all made it out safely I assume?"

"Yea." She begrudgingly replied.

"The body frame, arms, legs and hand tell a lot about a person. So how long did it take you to solve the case?" the man asked his neighbour.

"Now I feel ashamed to say this, but I am not the one who solved it."

Sera Masumi watched her neighbour crooked his eyebrow as he listened to her reply.

"Then who was the one?"

Masumi considered her response, she wanted to keep the name Kudo Shinichi out as he has been trying to maintain a low profile in public, and her neighbour in this case counts as a member of the public. She does not want to say a child named 'Edogawa Conan' solved the case.

"An acquaintance of mine." was her reply in the end.

"I see. Did he or she visit the crime scene?"

"Not at all. He seemed to have solved it from some photos."

"So he solved it just from some photos…interesting."

"We have to go." The child interrupted, her voice was too deep and mature for a mere child, there was also a certain tone of authority in her voice. A suppressed cough followed her sentence.

"Are you going out to get dinner too?" Sera Masumi asked her neighbour.

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><p>I was appalled that none of the main characters noticed how oddly shaped the '死' character was, I guess they were forced to ignore that because the Aoyama Gosho wanted to drag the case on for some plot revelant issues, or maybe it was because Japanese people don't write enough Kanji to notice it. Kanji characters are basically characters borrowed from the Chinese language, I guessed I noticed it quickly because I know how to write Chinese. I can only adapt chapters in which I can find a way for my OC to solve the case before the main characters do, but I am nowhere as smart as my OC and I have no idea when I will feel smart enough again to write the next chapter...in the meantime if I have more time to write fanfictions it will probably be my about other DC fic which is more for people who like ridiculous and low-intelligence contents...<p>

Thank you for reading, please leave a review.


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